diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,78 @@
+VIM LICENSE
+
+I)  There are no restrictions on distributing unmodified copies of Vim except
+    that they must include this license text.  You can also distribute
+    unmodified parts of Vim, likewise unrestricted except that they must
+    include this license text.  You are also allowed to include executables
+    that you made from the unmodified Vim sources, plus your own usage
+    examples and Vim scripts.
+
+II) It is allowed to distribute a modified (or extended) version of Vim,
+    including executables and/or source code, when the following four
+    conditions are met:
+    1) This license text must be included unmodified.
+    2) The modified Vim must be distributed in one of the following five ways:
+       a) If you make changes to Vim yourself, you must clearly describe in
+          the distribution how to contact you.  When the maintainer asks you
+          (in any way) for a copy of the modified Vim you distributed, you
+          must make your changes, including source code, available to the
+          maintainer without fee.  The maintainer reserves the right to
+          include your changes in the official version of Vim.  What the
+          maintainer will do with your changes and under what license they
+          will be distributed is negotiable.  If there has been no negotiation
+          then this license, or a later version, also applies to your changes.
+          The current maintainers are listed here: https://github.com/orgs/vim/people.
+          If this changes it will be announced in appropriate places (most likely
+          vim.sf.net, www.vim.org and/or comp.editors). When it is completely
+          impossible to contact the maintainer, the obligation to send him
+          your changes ceases.  Once the maintainer has confirmed that he has
+          received your changes they will not have to be sent again.
+       b) If you have received a modified Vim that was distributed as
+          mentioned under a) you are allowed to further distribute it
+          unmodified, as mentioned at I).  If you make additional changes the
+          text under a) applies to those changes.
+       c) Provide all the changes, including source code, with every copy of
+          the modified Vim you distribute.  This may be done in the form of a
+          context diff.  You can choose what license to use for new code you
+          add.  The changes and their license must not restrict others from
+          making their own changes to the official version of Vim.
+       d) When you have a modified Vim which includes changes as mentioned
+          under c), you can distribute it without the source code for the
+          changes if the following three conditions are met:
+          - The license that applies to the changes permits you to distribute
+            the changes to the Vim maintainer without fee or restriction, and
+            permits the Vim maintainer to include the changes in the official
+            version of Vim without fee or restriction.
+          - You keep the changes for at least three years after last
+            distributing the corresponding modified Vim.  When the maintainer
+            or someone who you distributed the modified Vim to asks you (in
+            any way) for the changes within this period, you must make them
+            available to him.
+          - You clearly describe in the distribution how to contact you.  This
+            contact information must remain valid for at least three years
+            after last distributing the corresponding modified Vim, or as long
+            as possible.
+       e) When the GNU General Public License (GPL) applies to the changes,
+          you can distribute the modified Vim under the GNU GPL version 2 or
+          any later version.
+    3) A message must be added, at least in the output of the ":version"
+       command and in the intro screen, such that the user of the modified Vim
+       is able to see that it was modified.  When distributing as mentioned
+       under 2)e) adding the message is only required for as far as this does
+       not conflict with the license used for the changes.
+    4) The contact information as required under 2)a) and 2)d) must not be
+       removed or changed, except that the person himself can make
+       corrections.
+
+III) If you distribute a modified version of Vim, you are encouraged to use
+     the Vim license for your changes and make them available to the
+     maintainer, including the source code.  The preferred way to do this is
+     by e-mail or by uploading the files to a server and e-mailing the URL.
+     If the number of changes is small (e.g., a modified Makefile) e-mailing a
+     context diff will do.  The e-mail address to be used is
+     <maintainer@vim.org>
+
+IV)  It is not allowed to remove this license from the distribution of the Vim
+     sources, parts of it or from a modified version.  You may use this
+     license for previous Vim releases instead of the license that they came
+     with, at your option.
diff --git a/README.md b/README.md
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index 0000000..ed98da1
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+++ b/README.md
@@ -0,0 +1,22 @@
+# .jjdescription files plugin for Vim
+This plugin adds syntax highlighting and some sensible options for
+.jjdescription files. These are temporary files created by [JJ][1] and opened
+in your configured editor when you run `jj describe`, so you can write a
+description for your change.
+
+## Installation
+Use your favorite plugin manager to install the `avm99963/vim-jjdescription`
+plugin. For instance, with [vim-plug][2] you should add the following to the
+appropriate section in your `.vimrc`:
+
+``` vimscript
+Plug 'avm99963/vim-jjdescription'
+```
+
+## Credits
+This plugin is based on the native syntax highlighting and ftplugin for
+gitcommit, which is the format of the analogous temporary files used by Git.
+This is the reason why this plugin is licensed with the Vim license.
+
+[1]: https://github.com/martinvonz/jj
+[2]: https://github.com/junegunn/vim-plug
diff --git a/ftdetect/jjdescription.vim b/ftdetect/jjdescription.vim
new file mode 100644
index 0000000..fd1f7a2
--- /dev/null
+++ b/ftdetect/jjdescription.vim
@@ -0,0 +1 @@
+au BufRead,BufNewFile *.jjdescription set filetype=jjdescription
diff --git a/ftplugin/jjdescription.vim b/ftplugin/jjdescription.vim
new file mode 100644
index 0000000..f45a55e
--- /dev/null
+++ b/ftplugin/jjdescription.vim
@@ -0,0 +1,21 @@
+" jjdescription filetype plugin
+" Language:	jjdescription file
+" Maintainer:	Adrià Vilanova <me@avm99963.com>
+" Source: Based on ftplugin/gitcommit.vim
+" Last Change:	2024 Jan 30
+
+" Only do this when not done yet for this buffer
+if (exists("b:did_ftplugin"))
+  finish
+endif
+
+let b:did_ftplugin = 1
+
+setlocal nomodeline tabstop=8 formatoptions+=tl textwidth=72
+setlocal formatoptions-=c formatoptions-=r formatoptions-=o formatoptions-=q formatoptions+=n
+setlocal formatlistpat=^\\s*\\d\\+[\\]:.)}]\\s\\+\\\|^\\s*[-*+]\\s\\+
+
+let b:undo_ftplugin = 'setl modeline< tabstop< formatoptions< tw< com< cms< formatlistpat<'
+
+let &l:comments = ':JJ: '
+let &l:commentstring = 'JJ: %s'
diff --git a/syntax/jjdescription.vim b/syntax/jjdescription.vim
new file mode 100644
index 0000000..de3de98
--- /dev/null
+++ b/syntax/jjdescription.vim
@@ -0,0 +1,52 @@
+" jjdescription syntax file
+" Language:	jjdescription file
+" Maintainer:	Adrià Vilanova <me@avm99963.com>
+" Filenames:	*.jjdescription
+" Source: Based on syntax/gitcommit.vim
+" Last Change:	2024 Jan 30
+
+if exists("b:current_syntax")
+  finish
+endif
+
+scriptencoding utf-8
+
+syn case match
+syn sync minlines=50
+syn sync linebreaks=1
+
+if has("spell")
+  syn spell toplevel
+endif
+
+if get(g:, 'jjdescription_summary_length') < 0
+  syn match   jjdescriptionSummary	"^.*$" contained containedin=jjdescriptionFirstLine nextgroup=jjdescriptionOverflow contains=@Spell
+elseif get(g:, 'jjdescription_summary_length', 1) > 0
+  exe 'syn match   jjdescriptionSummary	"^.*\%<' . (get(g:, 'jjdescription_summary_length', 50) + 1) . 'v." contained containedin=jjdescriptionFirstLine nextgroup=jjdescriptionOverflow contains=@Spell'
+endif
+syn match   jjdescriptionOverflow	".*" contained contains=@Spell
+syn match   jjdescriptionBlank	"^.\+" contained contains=@Spell
+syn match   jjdescriptionFirstLine	"\%^.*" nextgroup=jjdescriptionBlank,jjdescriptionComment skipnl
+
+syn match   jjdescriptionComment "^JJ: .*"
+
+syn match   jjdescriptionHeader	"\%(^JJ: \)\@<=\S.*:\%(\n^$\)\@!$" contained containedin=jjdescriptionComment
+
+syn match   jjdescriptionType		"\%(^JJ:\s\+\)\@<=[MADR]\ze " contained containedin=jjdescriptionComment nextgroup=jjdescriptionFile skipwhite
+syn match   jjdescriptionFile		".*" contained
+
+syn region  jjdescriptionSelected	start=/^\z(^JJ: \)This commit contains the following changes:$/ end=/^\z1$\|^\z1\@!/ contains=jjdescriptionHeader,jjdescriptionSelectedType containedin=jjdescriptionComment containedin=jjdescriptionComment contained transparent fold
+
+syn match   jjdescriptionSelectedType		"\%(^JJ:\s\+\)\@<=[MADR]\ze " contained nextgroup=jjdescriptionSelectedFile skipwhite
+syn match   jjdescriptionSelectedFile	".*" contained
+
+hi def link jjdescriptionSummary		Keyword
+hi def link jjdescriptionComment		Comment
+hi def link jjdescriptionSelectedType	jjdescriptionType
+hi def link jjdescriptionType		Type
+hi def link jjdescriptionHeader		PreProc
+hi def link jjdescriptionSelectedFile	jjdescriptionFile
+hi def link jjdescriptionFile		Constant
+hi def link jjdescriptionBlank		Error
+
+let b:current_syntax = "jjdescription"